Sewing machines are equipped with presser bar and presser foot assemblies to press the work piece against the throat plate and the feed dog so that a good needle loop will be formed, and so that the feed dog will carry the material the desired distance between needle penetrations. Many of the inexpensive consumer sewing machines have a presser bar that applies a nonadjustable pressure chosen by the machine manufacturer as the best average setting for common materials. In more expensive machines, manual means may be provided to allow the user to control the presser bar pressure to optimize the pressure for any material being sewn.
Sewing machines now available in which the pattern stitching is electronically controlled include memory devices and electronic logic circuits capable of producing electronic signals for controlling sewing machine functions. It has been suggested that presser bar pressure could be actuated directly by a solenoid controlled, in turn, by electronic signals from such logic circuits. However, the magnitude of force required is so high that the power to operate such direct-acting solenoids is excessive. In addition, their reaction times are too slow.